Species-specific recognition of beetle cues by the nematode Pristionchus maupasi.

The environment has a strong effect on development as is best seen in the various examples of phenotypic plasticity. Besides abiotic factors, the interactions between organisms are part of the adaptive forces shaping the evolution of species. To study how ecology influences development, model organisms have to be investigated in their environmental context. We have recently shown that the nematode Pristionchus pacificus and its relatives are closely associated with scarab beetles with a high degree of species specificity. For example, P. pacificus is associated with the oriental beetle Exomala orientalis in Japan and the northeastern United States, whereas Pristionchus maupasi is primarily isolated from cockchafers of the genus Melolontha in Europe. Here, we investigate how Pristionchus nematodes identify their specific insect hosts by using chemotaxis studies originally established in Caenorhabditis elegans. We observed that P. maupasi is exclusively attracted to phenol, one of the sex attractants of Melolontha beetles, and that attraction was also observed when washes of adult beetles were used instead of pure compounds. Furthermore, P. maupasi chemoattraction to phenol synergizes with plant volatiles such as the green leaf alcohol and linalool, demonstrating that nematodes can integrate distinct chemical senses from multiple trophic levels. In contrast, another cockchafer-associated nematode, Diplogasteriodes magnus, was not strongly attracted to phenol. We conclude that interception of the insect communication system might be a recurring strategy of Pristionchus nematodes but that different nematodes use distinct chemical cues for finding their beetle hosts.